The objective of the proposed research is to study the relationship between the oxygen tension in the distal segment of the optic nerve and its function. The analysis will be carried out by studying the effect of changes in the perfusion pressure of the optic disk circulation, alteration in the circulation by selective vascular occlusions, sympathetic nerve supply interruption and stimulation and the study of the effect of the administration of autonomic drugs. A micro oxygen electrode is placed in the optic disk of rhesus monkeys. The optic nerve discharge is monitored by placing an electrode in the intracranial portion of the nerve in front of the chiasm. The perfusion pressure is altered by changing the systemic blood pressure and/or the intraocular pressure. The cervical sympathetic chain is either sectioned in a chronic preparation or stimulated and the effect on the optic disk oxygen tension and optic nerve function measured. The effect of autonomic drugs is studied following their systemic and local administration.